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TPSM8D6C24: How to make sure VDD5 is powered by external supply

Kazuki Itoh
Genius 11010 points
Part Number: TPSM8D6C24


Hi team,

 

Could you please let me know how to make sure VDD5 is powered by external supply?

The datasheet 7.3.2 mentions the external supply should be higher voltage than the LDO regulation voltage programmed by (B5h) USER_DATA_05 (POWER_STAGE_CONFIG).

 

In default, the maximum LDO regulation voltage looks like 4.9V.

 

Looking at Figure 7-4, I wonder how we can know that VDD5 is working with external supply because the forward voltage of the diode should be considered.

 

 

If the maximum forward voltage of the diode is 0.35V, should the anode voltage (i.e. external power supply voltage setting) be calculated as below?

 Vin_max+ Vf_max = 4.9+0.35 = 5.25[V]

 

I wonder why 4.75V-5.25V anode voltage is enough to operate external VDD5 considering the forward voltage drop.

I think this is important for efficient power design.

 

Best regards,

Itoh

 

  • 0
    TI__Guru 56985 points

     

    If the customer needs to ensure that the external 5V is powering VDD5, the internal LDO voltage can be programmed to 4.3V instead of 4.7V using the Power Stage Config command.  The LDO defaults to 4.7V to provide good efficiency when no external 5V is available.

  • 0 in reply to Peter James Miller
    TI__Genius 11010 points

    Hi Peter-san,

     

    My customer’s application is efficiency sensitive (has fully enclosed structure which has limited pass to dissipate the heat), so they want to increase the efficiency as much as possible.

    Also, they wan to use TPSM8D6C24 without the external controller, so they don’t want to use register setting (SEL_VDD5).

    Could you suggest any alternative solution?

     

    Regards,

    Itoh

  • +1 in reply to Kazuki Itoh
    TI__Guru 56985 points

     

    For the best efficiency, they should power AVIN and VDD5 from the same external 5V source, then no diode is required and the IC will be more efficient than powering AVIN from 12V and VDD5 from 5V.

    I would recommend they power the VDD5 voltage directly and use a 10Ω Resistor with 1.0μF bypass capacitor to filter AVIN from that common 5V source.

    If they happen to also have a 3.3V supply, they can squeeze out a tiny bit of additional efficiency by powering AVIN from the 3.3V and VDD5 from the 5V, that configuration also does not need a diode.

  • +1 in reply to Kazuki Itoh
    TI__Guru 56985 points

    Follow Figure 7-3 from the datasheet.